Recently, optical modulators and waveguides have garnered increased attention for a variety of applications, especially in data transmission, processing, and interconnects, with the thrust towards nanophotonics. One application of optical modulators is the transmission of information on computer chips. The trend is toward using wavelength division multiplexing (WDM) to transmit data in an optical system. WDM is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths, i.e., different colors of light, to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fiber. Optical modulators that may be used for WDM systems have the ability to modulate at specific wavelengths. However, conventional optical modulators are generally less wavelength sensitive. Modulators that are fabricated from lithium niobate generally are broadband and can modulate at different wavelengths, ranging from infrared to visible. But, these modulators, like other modulators, such as electro-absorption and micro-ring, suffer from issues in material compatibilities, optical coupling issues, and are complex to fabricate. Thus, due to the limitations of conventional optical modulators and other components of the conventional optical transmission system, such as detectors, different nano-wavelengths of light may not be used for the transmission of information.
One form of optical modulator, Schottky barrier modulators, typically include a semiconductor, such as silicon, or any III-V material such as GaAs, InP, AlGaAs, InGaAsP, GaN, InGaN, with an over-lying metal Schottky electrode. The interface between the semiconductor and the Schottky electrode is known as the Schottky energy barrier. In a Schottky modulator, carriers are generated in the semiconductor by forward-biasing the modulator. That is, a positive potential is applied to the metal with respect to the n-type semiconductor for generating carriers and changing the refractive index of the semiconductor. This, in turn, changes the wavelength of light that is permitted to pass through the subwavelength nano-holes in the metal. Depending on the incident wavelength, such as near infrared, the metal can be replaced with a highly delta doped p layer with subwavelength nano-hole arrays.
Conventional optical modulators, including lithium niobate electro-optic modulators, III-V electro-absorption modulators, and silicon micro-ring modulators, all suffer from several other drawbacks as well. First, conventional optical modulators incorporating wavelength selectivity are relatively difficult to fabricate. The wavelength selectivity in these modulators is usually accomplished by either precision growth of III-V epitaxial films such as III-V electro-absorption modulators or complex fabrication techniques to generate extremely smooth curved surfaces in silicon and coupling out with an optical waveguide in the case of silicon micro-ring modulators. This is a very limiting factor in applications where space is a premium or the need for low cost is important, such as applications for computer chips. Second, the complex fabrication process used for conventional optical modulators is excessively time-consuming and expensive. Moreover, inexpensive conventional optical modulators, such as lithium niobate modulators, do not allow selected wavelengths of light to be modulated.